\begin{itemize}
\item The current system only supports scalar variables and scalar-valued expressions.
\item Internally, an expression is stored as a tree.
\begin{center}
\includegraphics[width=0.6\textwidth]{poster/expr}
\end{center}
The tree above corresponds to the following mathematical expression:
\begin{equation*}
|x-3|+e^x \; .
\end{equation*}
\item Convexity or concavity of an expression is not tested at construction time, so one can construct arbitrary expressions.
\end{itemize}
